One goal of device testing is to measure the noise contributed by that device to a circuit in which the device is a component. For example, the noise factor or noise figure of a device under test (DUT) such as an amplifier that is characterized by a voltage gain and noise power spectral density, NA is one way of characterizing the noise contribution provided by the DUT. Another goal of device testing is to monitor the noise contribution of the DUT while operational signals are passing through the DUT rather than test signals.
Methods for making such noise measurements utilize experimental setups that also introduce noise into the measurements; hence, some method must be used to separate out the noise contributions introduced by the measurement apparatus itself from that contributed by the DUT. Methods that rely on calibrations of the measurement apparatus are known to the art. The calibration processes, however, are time consuming and can limit the accuracy of the DUT measurements. In addition, the DUT measurements are limited to the signals that are provided by the measurement equipment in the configuration provided by the measurement apparatus. These measurements may not accurately represent the noise performance of the DUT in the actual circuit operating with operational signals that are used with the real circuit.